事情得從一個報告說起，有人說網頁map.yahoo.co.jp，在IE中進行打印預覽時，使用倍率666%會讓IE崩潰（至少2016-5-28為止還是這樣），為什么IE中會出現這么6的問題呢？從打印預覽這個功能看起吧。
從網頁的角度來看，負責打印預覽的相關內容位于res://ieframe.dll/preview.dlg與res://ieframe.dll/preview.js。IE自5.5開始引入了打印預覽以及自定義的打印預覽功能。而微軟的早期文檔內容十分豐富，可以參考到很多有用信息。
在雅虎網站造成IE的崩潰中，一步不可缺少的操作是——設置縮放比例。所以，我們的關注點可以集中到縮放比率上。
在MSDN介紹自定義打印預覽模板時，微軟提到：“推薦使用一個DIV作為主容器”。在preview.dlg的LN253-256，可以看到MasterContainer，是一個DIV，這也與微軟的推薦做法一致。
#!html
<div id="MasterContainer" tabindex="0" style="width:100%; position:absolute;" >
<!-- Pages go here -->
<div id="EmptyPage" class="divPage" style="position:absolute; left:0px; top:0px; display:none;"><div class="page"> </div></div>
</div>
另外，還“推薦使用CSS的zoom屬性來為主容器設置百分比的縮放”，這在preview.js中得到了良好的體現：
#!js
function PositionPages(nDispPage) {
……
MasterContainer.style.zoom = g_nZoomLevel + "%";
……
與：
#!js
function ChangeZoom() {
MasterContainer.style.zoom = g_nZoomLevel + "%";
PositionPages(g_nDispPage);
return g_nZoomLevel;
}
在了解了縮放功能進行縮放的方法之后，讓我們再看一看頁面是如何被轉入預覽中的。
在preview.js的CPrintDoc_AddPage()函數中，可以看到如下的代碼注入到了MasterContainer的beforeEnd處。
#!js
newHTM = "<DIV class=divPage><IE:DeviceRect media=\"print\" class=page id=mDiv" + this._nStatus + this._strDoc + "p" + aPage.length + ">";
newHTM += "<IE:LAYOUTRECT id=mRect" + this._nStatus + this._strDoc + "p" + aRect.length;
newHTM += " class='" + classLayoutRect + "' nextRect=mRect" + this._nStatus + this._strDoc + "p" + (aRect.length + 1);
newHTM += " onlayoutcomplete=\"OnRectComplete('" + this._strDoc + "', " + g_ObsoleteBar + ")\"";
newHTM += " tabindex=-1 onbeforefocusenter='event.returnValue=false;' ";
newHTM += " />";
newHTM += "<DIV class='" + classHeader + "' id=header>";
newHTM += HeadFoot.HtmlHead;
newHTM += "</DIV>";
newHTM += "<DIV class='" + classFooter + "' id=footer>";
newHTM += HeadFoot.HtmlFoot;
newHTM += "</DIV>";
newHTM += "</IE:DeviceRect></DIV>";
MasterContainer.insertAdjacentHTML("beforeEnd", newHTM);
在上面的代碼中可以看到一些特殊的元素。比如IE:DEVICERECT和IE:LAYOUTRECT。DeviceRect、LayoutRect兩個元素用來組合展示頁面。每個DeviceRect代表一個頁面，
LayoutRect為DeviceRect的子元素，IE在它里面顯示頁面預覽。因為preview.dlg指定了XML Namespace（<HTML XMLNS:IE>）所以元素前帶有IE:前綴。
與其他元素不同的是，LayoutRect似乎并沒有innerHTML屬性。IE只是在里面展示頁面的預覽，頁面并不能操作它。那么問題來了，IE怎么產生的預覽？
要知道這個，讓我們先完整地跟蹤整個流程。首先，因為打印預覽是在res: protocol下的，之前的文章我們介紹了CResProtocol是處理Res Protocol的類，在DoParseAndBind上下斷點可以觀察到此處完整的調用（無關的棧已經刪除）：
#!bash
0:058> bp MSHTML!CResProtocol::DoParseAndBind
0:牌058> g
Breakpoint 0 hit
eax=14061280 ebx=140611fc ecx=08101bd4 edx=1406127c esi=76c2f1fc edi=120ae270
eip=6474f8dd esp=120ae258 ebp=120ae290 iopl=0 nv up ei pl zr na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000246
MSHTML!CResProtocol::DoParseAndBind:
6474f8dd 8bff mov edi,edi
0:058> kvn
# ChildEBP RetAddr Args to Child
00 120ae254 647504d6 14061280 14061284 14061274 MSHTML!CResProtocol::DoParseAndBind (FPO: [4,163,4])
01 120ae268 64750495 120ae2b0 64750410 140611e0 MSHTML!CResProtocol::ParseAndBind+0x26 (FPO: [0,0,0])
02 120ae290 76c63067 140611fc 06e8c9f0 08109f38 MSHTML!CResProtocol::Start+0x88 (FPO: [6,5,4])
…………………………
10 120aeeb4 6467517a 120aeed0 00000000 00000000 MSHTML!CMarkup::Load+0x228 (FPO: [1,71,4])
11 120af26c 6479f0a1 120af2a0 00000000 00000000 MSHTML!CMarkup::LoadFromInfo+0xb07 (FPO: [Non-Fpo])
12 120af3b0 6479ebf4 120af3d8 00000000 120af490 MSHTML!CDoc::LoadFromInfo+0x48d (FPO: [Non-Fpo])
13 120af474 65075c07 03ea5400 00000001 081d4de0 MSHTML!CDoc::Load+0xd7 (FPO: [5,41,4])
14 120af5ec 650772d6 120af678 120af668 080940c8 MSHTML!CHTMLDlg::Create+0x869 (FPO: [Non-Fpo])
15 120af65c 6507e39d 00000000 10908ed0 00000000 MSHTML!InternalShowModalDialog+0x1c1 (FPO: [Non-Fpo])
16 120af718 6507e54d 120af770 6629d470 0000000b MSHTML!ModelessThreadInit+0x12f (FPO: [Non-Fpo])
……………………
根據15層棧可以知道該窗口是一個Modeless Window，那么這個調用是誰發起的呢？觀察其他線程，可以發現下列調用棧（無關棧已經刪除）：
#!bash
43 Id: 5404.3b18 Suspend: 1 Teb: 7ef7e000 Unfrozen
# ChildEBP
…………………………
06 10908f58 6507a498 1449d3c0 054b8f94 081a995c MSHTML!InternalModelessDialog+0x431 (FPO: [Non-Fpo])
07 10908fe8 6655f9b0 00a62528 081d4de0 000003e0 MSHTML!ShowHTMLDialogEx+0xa8 (FPO: [6,32,0])
08 109095b4 6649aafe 10909728 00000000 00000001 IEFRAME!CDocHostUIHandler::DoTemplatePrinting+0x31d (FPO: [Non-Fpo])
09 10909688 650587fb 08260e7c 6464d428 00000007 IEFRAME!`Microsoft::WRL::Module<1,Microsoft::WRL::Details::DefaultModule<1> >::Create'::`2'::`dynamic atexit destructor for 'module''+0x64146
0a 10909b94 648662de 0a4d2b40 00000000 00000000 MSHTML!CDoc::PrintHandler+0x73a (FPO: [Non-Fpo])
0b 1090a7a8 6464dea1 00000000 663d9884 000007d3 MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0xbdfbd
0c 1090a7c8 66562101 03ea3f00 663d9884 000007d3 MSHTML!CDoc::Exec+0x21 (FPO: [6,0,0])
0d 1090ba08 66568f04 080fd650 00000000 1090ba70 IEFRAME!CDocHostUIHandler::ShowContextMenu+0x98d (FPO: [5,1157,4])
0e 1090ba3c 64f4aaac 004bc898 00000000 1090ba70 IEFRAME!CDocObjectHost::ShowContextMenu+0xd4 (FPO: [Non-Fpo])
0f 1090ba80 64f7ed1f 00000123 000000d7 00000000 MSHTML!CDoc::ShowContextMenu+0x137 (FPO: [4,7,4])
10 1090ba9c 64f7dbe6 00000123 000000d7 00000000 MSHTML!CElement::ShowContextMenu+0x1f (FPO: [Non-Fpo])
11 1090bc00 64eb5e79 1090bd78 00000000 64647180 MSHTML!CElement::OnContextMenu+0x17b (FPO: [2,81,4])
12 1090bc50 64bb244c 0a58da40 1090bd78 1090bd78 MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0xb62fa
13 1090bc70 645c789e 0a58da40 1090bd78 03ea3f00 MSHTML!CElement::HandleMessage+0xc2 (FPO: [Non-Fpo])
14 1090bc90 645c7430 14054840 0000007b 03ea3f00 MSHTML!CElement::HandleWindowMessage+0x6b (FPO: [Non-Fpo])
15 1090bd1c 647e7558 1090bd78 14054840 00000000 MSHTML!CDoc::PumpMessage+0x638 (FPO: [3,29,4])
16 1090be94 64cee296 0000007b 00a62528 00d70123 MSHTML!CDoc::OnMouseMessage+0x2b4 (FPO: [7,85,4])
…………………………
可以發現
有了之前的結論之后，首先來觀察MSHTML!CDoc::PrintHandler。在IDA中打開MSHTML.DLL，定位到CDoc::PrintHandler后查看偽代碼（下為Win7+IE11的結果）。
首先CDoc::PrintHandler檢查指定的CLSID是否被支持。下偽代碼實際含義pCommandTarget->Exec(&CGID_DocHostCommandHandler, a10（即：guid）, a7, &varIn （即：v73）, &varOut （即：v67）); 。
#!cpp
if ( pCommandTarget && a7 != 2 && !(*(_DWORD *)(v10 + 3584) & 0x400000) )
{
hr = (*(int (__stdcall **)(int, const GUID *, int, int, int, int *))(*(_DWORD *)pCommandTarget + 16))(
pCommandTarget,
&CGID_DocHostCommandHandler,
(a10 != 0) + 6,
a7,
v73,
v67);
v11 = hr;
if ( hr != OLECMDERR_E_NOTSUPPORTED && hr != OLECMDERR_E_UNKNOWNGROUP && hr != OLECMDERR_E_DISABLED)
goto Cleanup;
v12 = v72;
}
接著，程序尋找是否有alternative print source，也即由<link>元素的REL=alternate MEDIA=print指定的其他可選打印源。如果沒有，做一些簡單的字符串處理工作：
#!cpp
if ( !CDoc::GetAlternatePrintDoc((const unsigned __int16 *)v71, v12, (unsigned __int16 *)&v78, v12) )
{
v16 = &v78;
do
{
v17 = *(_WORD *)v16;
v16 += 2;
}
while ( v17 != (_WORD)v69 ); //wcslen
if ( (signed int)(v16 - (char *)&v79) >> 1 )
{
v15 = (int)&v78;
v71 = (int)&v78;
LABEL_14:
if ( !RatingEnabledQuery() )
{
v11 = 0x80004005u;
goto Cleanup;
}
goto LABEL_16;
}
}
再接下來是一個比較長的函數段。首先程序判斷是否有可打印的plugin site。例如acrobat pdf都算是這種。然后發送“Print”請求。MSDN解釋是“用默認模版或自定義模版”來打印（https://msdn.microsoft.com/en-us/library/aa769937(v=vs.85).aspx）。
#!cpp
v73 = 0;
if( !CDoc::GetPlugInSiteForPrinting(v72, &v73) )
{
v18 = v73;
if ( a10 )
{
v11 = -2147467259;
}
else
{
memset(&v50, 0, 0x20u);
v69 = 0;
Cookie = 0;
//發送IDM_PRINT請求
v11 = (*(int (__stdcall **)(int, GUID *, wchar_t **, signed int, LCID, ULONG_PTR *))(*(_DWORD *)v73 + 20))(
v73,
&GUID_NULL,
&off_6449DFC0, //"Print"
1,
g_lcidUserDefault,
&Cookie);
if ( v11 )
{
FreeEXCEPINFO(v46);
goto LABEL_70;
}
VariantInit(&pvarg);
v55 = 0;
v53 = 0;
v54 = 0;
//
v11 = (*(int (__stdcall **)(int, ULONG_PTR, GUID *, LCID, signed int, char *, VARIANTARG *, char *, int *))(*(_DWORD *)v18 + 24))(
v18,
Cookie,
&GUID_NULL,
g_lcidUserDefault,
1,
&v52,
&pvarg,
&v50,
&v69);
VariantClear(&pvarg);
FreeEXCEPINFO(v46);
}
LABEL_69:
ReleaseInterface((struct IUnknown *)v46);
goto LABEL_70;
}
然后，可以看到PrintHandler將當前頁面保存到了臨時目錄下。
#!cpp
CDoc::PrintHandler(CDocument *,ushort const *,ushort const *,ulong,tagSAFEARRAY *,ulong,tagVARIANT *,tagVARIANT *,int)
{
......
if ( !v71 )
{
CDoc::SetTempFileTracking(1);
Cookie = CDoc::HasTextSelection(v10);
CDoc::SaveToTempFileForPrint(
v72,
&v78,
260u,
Cookie != 0 ? (int)&v77 : 0,
Cookie != 0 ? 0x104 : 0,
Cookie != 0 ? (int)&v77 : 0);
CDoc::TransferTempFileList(&v56);
CDoc::SetTempFileTracking(0);
v71 = (int)&v78;
}
......
隨后，SetPrintCommandParameters、SetPrintManagerCommandParameters用來設置打印參數，先跳過不看，之后有一個關鍵操作CreateHTMLDocSource，則是負責彈出打印窗口的主人公。
#!cpp
v11 = CreateHTMLDocSource(v61, v39, v40, v38, (struct IInspectable **)v48, v49);
CreateHTMLDocSource代碼簡單明了，列舉如下：
#!cpp
HRESULT __fastcall CreateHTMLDocSource(int a1, int a2, int a3, struct IWebPlatformHostSecurityManagerFactory *a4, struct IInspectable **a5, bool a6)
{
HRESULT v6; // [email protected]
int v8; // [sp+4h] [bp-4h]@1
v8 = 0;
v6 = HTMLDocumentSource::Create((int)&v8, a1, a2, (char)a4);
if ( v6 >= 0 )
v6 = HTMLDocumentSource::QueryInterface(v8, &_GUID_af86e2e0_b12d_4c6a_9c5a_d7aa65101e90, a3);
TSmartPointer<HTMLDocumentSource>::_TSmartPointer<HTMLDocumentSource>(&v8);
return v6;
}
調用HTMLDocumentSource::Create并QueryInterface并返回在參數a3中。查看HTMLDocumentSource::Create的代碼，也是一個短小的函數：
#!cpp
HRESULT __fastcall HTMLDocumentSource::Create(int a1, int a2, int a3, char a4)
{
int v4; // [email protected]
int v5; // [email protected]
LPVOID v6; // [email protected]
int v7; // [email protected]
HRESULT v8; // [email protected]
int v10; // [sp+Ch] [bp-4h]@4
v4 = a2;
v5 = a1;
v6 = HeapAlloc(g_hProcessHeap, 0, 0x60u);
if ( v6 )
v7 = HTMLDocumentSource::HTMLDocumentSource(v6);
else
v7 = 0;
v10 = v7;
if ( v7 )
{
v8 = HTMLDocumentSource::_Initialize((void *)v7, v4, a3, a4);
if ( v8 >= 0 )
{
v10 = 0;
*(_DWORD *)v5 = v7;
}
}
else
{
v8 = -2147024882;
}
TSmartPointer<HTMLDocumentSource>::_TSmartPointer<HTMLDocumentSource>(&v10);
return v8;
}
函數創建HTMLDocumentSource類，并調用_Initialize函數進行初始化。構造函數的代碼簡單易懂，全部都是賦初值的，跳過不敘述了。接下來查看_Initialize。
_Initialize是一個較長的函數，但是邏輯較為清晰，我把所有IDA沒有識別出的guid等全部以注釋的形式標記了。該函數先獲取了IHTMLEventObj2接口，然后識別環境并設置瀏覽模式為__IE_Immersive（Win8 Immersive Mode），若Immersive Mode生效，再設置成__IE_ShrinkToFit（Shrink to fit模式，該模式下瀏覽器自動將頁面收縮成方便打印的大小）模式。
然后，調用PrintManagerOptions::Create。這個操作將創建一個PrintManagerOptions對象，并調用其_Initialize方法，干的事情也就是拿到它的IUnkonwn接口，所以這塊我們也跳過。
接下來，IE試圖打開“res://ieframe.dll/preview.dlg”，很熟悉的字眼。告知該處理程序臨時文件位置等設置。
#!cpp
HRESULT __thiscall HTMLDocumentSource::_Initialize(void *this, int a2, int a3, char a4)
{
int v4; // [email protected]
LPVOID *v5; // [email protected]
HRESULT v6; // [email protected]
int v7; // [email protected]
IUnknown *v8; // [email protected]
LPUNKNOWN *v9; // [email protected]
int v10; // [email protected]
int v11; // [email protected]
int v12; // [email protected]
const WCHAR *v13; // [email protected]
BSTR v14; // [email protected]
LPMONIKER v15; // [email protected]
struct IMonikerVtbl *v16; // [email protected]
LONG v18; // [sp-4h] [bp-130h]@23
struct HTMLDLGINFO *v19; // [sp+0h] [bp-12Ch]@24
int v20; // [sp+4h] [bp-128h]@24
int Dst; // [sp+10h] [bp-11Ch]@24
LPMONIKER v22; // [sp+14h] [bp-118h]@24
VARIANTARG *v23; // [sp+20h] [bp-10Ch]@24
char v24; // [sp+28h] [bp-104h]@26
int *v25; // [sp+2Ch] [bp-100h]@24
int v26; // [sp+30h] [bp-FCh]@24
char v27; // [sp+38h] [bp-F4h]@26
int v28; // [sp+48h] [bp-E4h]@24
int v29; // [sp+60h] [bp-CCh]@24
int v30; // [sp+70h] [bp-BCh]@24
int v31; // [sp+74h] [bp-B8h]@24
int v32; // [sp+78h] [bp-B4h]@24
int v33; // [sp+7Ch] [bp-B0h]@24
BSTR v34; // [sp+80h] [bp-ACh]@24
int v35; // [sp+84h] [bp-A8h]@24
VARIANTARG pvargSrc; // [sp+88h] [bp-A4h]@14
int v37; // [sp+98h] [bp-94h]@5
int v38; // [sp+9Ch] [bp-90h]@5
int v39; // [sp+A0h] [bp-8Ch]@5
int v40; // [sp+A4h] [bp-88h]@5
int v41; // [sp+A8h] [bp-84h]@14
int v42; // [sp+ACh] [bp-80h]@14
LPCWSTR szURL; // [sp+B0h] [bp-7Ch]@14
int v44; // [sp+B4h] [bp-78h]@14
int *v45; // [sp+B8h] [bp-74h]@13
int v46; // [sp+BCh] [bp-70h]@1
VARIANTARG pvarg; // [sp+C0h] [bp-6Ch]@8
LPUNKNOWN punkOuter; // [sp+D4h] [bp-58h]@1
void *v49; // [sp+D8h] [bp-54h]@1
LPMONIKER ppmk; // [sp+DCh] [bp-50h]@21
LONG v51; // [sp+E0h] [bp-4Ch]@4
char v52; // [sp+E7h] [bp-45h]@5
char v53; // [sp+E8h] [bp-44h]@14
unsigned int v54; // [sp+124h] [bp-8h]@1
int v55; // [sp+12Ch] [bp+0h]@1
v54 = (unsigned int)&v55 ^ __security_cookie;
punkOuter = 0;
v4 = (int)this;
v46 = a3;
v49 = this;
v5 = (LPVOID *)TSmartPointer<CDCompLayer>::operator_((char *)this + 52);
v6 = CoCreateInstance(&CLSID_StdGlobalInterfaceTable, 0, 1u, &_GUID_00000146_0000_0000_c000_000000000046, v5); //guid of IGlobalInterfaceTable
if ( v6 >= 0 )
{
v7 = TSmartPointer<CDCompLayer>::operator_(&punkOuter);
v6 = HTMLDocumentSource::QueryInterface(v4, &_GUID_00000000_0000_0000_c000_000000000046, v7); //querying IID_IUnknown
if ( v6 >= 0 )
{
v8 = punkOuter;
v9 = (LPUNKNOWN *)TSmartPointer<CDCompLayer>::operator_(v4 + 56);
v6 = CoCreateFreeThreadedMarshaler(v8, v9);
if ( v6 >= 0 )
{
v51 = 0;
v10 = TSmartPointer<IDispEffectConvolveMatrix>::operator_(&v51);
v6 = (**(int (__stdcall ***)(int, GUID *, int))a2)(a2, &_GUID_3050f48b_98b5_11cf_bb82_00aa00bdce0b, v10); //getting IHTMLEventObj2
if ( v6 >= 0 )
{
v52 = 1;
v37 = 0;
v38 = 0;
v39 = 0;
v40 = 0;
if ( (*(int (__stdcall **)(LONG, _DWORD, _DWORD, int *))(*(_DWORD *)v51 + 32))(
v51,
L"__IE_Immersive",
0,
&v37) >= 0
&& (_WORD)v37 == 11
&& -1 == (_WORD)v39 )
{
*(_QWORD *)&pvarg.vt = 0i64;
*(_QWORD *)&pvarg.lVal = 0i64;
if ( (*(int (__stdcall **)(LONG, _DWORD, _DWORD, VARIANTARG *))(*(_DWORD *)v51 + 32))(
v51,
L"__IE_ShrinkToFit",
0,
&pvarg) < 0
|| pvarg.vt != 11
|| (v52 = 1, -1 != LOWORD(pvarg.lVal)) )
v52 = 0;
VariantClear(&pvarg);
}
v45 = (int *)((char *)v49 + 60);
v11 = TSmartPointer<PrintManagerOptions>::operator_((char *)v49 + 60);
LOBYTE(v12) = v52;
v6 = PrintManagerOptions::Create(v12, v11);
if ( v6 >= 0 )
{
v41 = 0;
v42 = 0;
szURL = 0;
v44 = 0;
memcpy(&v53, L"res://ieframe.dll/preview.dlg", 0x3Cu);
*(_QWORD *)&pvargSrc.vt = 0i64;
*(_QWORD *)&pvargSrc.lVal = 0i64;
if ( (*(int (__stdcall **)(LONG, _DWORD, _DWORD, VARIANTARG *))(*(_DWORD *)v51 + 32))(
v51,
L"__IE_TemporaryFiles",
0,
&pvargSrc) >= 0
&& pvargSrc.vt == 8200 )
VariantCopy((VARIANTARG *)((char *)v49 + 72), &pvargSrc);
if ( (*(int (__stdcall **)(_DWORD, _DWORD, _DWORD, int *))(*(_DWORD *)v51 + 32))(
v51,
L"__IE_TemplateUrl",
0,
&v41) < 0
|| (_WORD)v41 != 8
|| (v13 = szURL) == 0 )
v13 = (const WCHAR *)&v53;
ppmk = 0;
v6 = CreateURLMonikerEx(0, v13, &ppmk, 1u);
if ( v6 >= 0 )
{
*(_QWORD *)&pvarg.vt = 0i64;
*(_QWORD *)&pvarg.lVal = 0i64;
pvarg.vt = 13;
v6 = PrintManagerOptions::QueryInterface(
*v45,
&_GUID_00000000_0000_0000_c000_000000000046,
(int)&pvarg.lVal);
if ( v6 >= 0 )
{
v18 = 0;
v6 = (*(int (__stdcall **)(LONG, _DWORD, _DWORD, _DWORD, LONG, _DWORD, _DWORD))(*(_DWORD *)v51 + 28))(
v51,
L"__PE_PrintManagerOptions",
*(_DWORD *)&pvarg,
*(_DWORD *)&pvarg.wReserved2,
pvarg.lVal,
HIDWORD(pvarg.dblVal),
0);
if ( v6 >= 0 )
{
VariantClear(&pvarg);
pvarg.vt = 13;
pvarg.lVal = v51;
v18 = v51;
(*(void (__stdcall **)(LONG))(*(_DWORD *)v51 + 4))(v51);
HTMLDLGINFO::HTMLDLGINFO(&Dst);
v32 = 0;
v33 = 0;
v34 = 0;
v35 = 0;
LOWORD(v32) = 8;
v14 = SysAllocString(0);
Dst = 0;
v29 = 0;
v34 = v14;
v22 = ppmk;
v23 = &pvarg;
v25 = &v32;
v28 = 720;
v26 = 1;
v30 = 1;
v31 = v46;
v6 = InternalModelessDialog(v19, v20);
if ( v6 >= 0 )
*((_BYTE *)v49 + 88) = a4;
VariantClear((VARIANTARG *)&v32);
VariantClear((VARIANTARG *)&v27);
CStr::_Free(&v24);
}
}
VariantClear(&pvarg);
}
v15 = ppmk;
ppmk = 0;
if ( v15 )
{
v16 = v15->lpVtbl;
v18 = (LONG)v15;
v16->Release(v15);
}
VariantClear(&pvargSrc);
VariantClear((VARIANTARG *)&v41);
}
VariantClear((VARIANTARG *)&v37);
}
TSmartPointer<IMFGetService>::_TSmartPointer<IMFGetService>(&v51);
}
}
}
TSmartPointer<IMFGetService>::_TSmartPointer<IMFGetService>(&punkOuter);
return v6;
}
最后，通過InternalModelessDialog啟動該窗口實現預覽
#!cpp
HRESULT __usercall InternalModelessDialog<eax>(int a1<edx>, int a2<ecx>, HRESULT a3<esi>)
那么這個預覽窗口中顯示的文檔和其他的到底有什么不同呢？根據MSDN文檔的意思是：有點像禁止了Script的WebBrowser。代碼將Layout當作一個容器來顯示預覽后的內容。在Modeless Window中，我們不能F12，不能呼出右鍵菜單，怎么辦？我們有另一種方法——通過IE暴露的接口來取得整個窗口的DOM內容。
這個邏輯中，預覽的窗口標題為“打印預覽”。可以使用FindWindow找到對應的窗口并枚舉出正確的Server窗口，或是使用Spy++找到窗口的HWND（因為這里我們并不是寫一個通用的工具，所以怎么方便怎么來）。
注意目標窗口是Internet Explorer_Server而不是外層的Internet Explorer_TridentDlgFrame。這里使用的代碼如下：
#!cpp
// prjFindPrintview.cpp : 定義控制臺應用程序的入口點。
//
#include "stdafx.h"
#include <Windows.h>
#include <mshtml.h>
#include <Exdisp.h>
#include <atlbase.h>
#include <SHLGUID.h>
#include <oleacc.h>
#include <comdef.h>
#include <tchar.h>
#pragma comment(lib, "Oleacc.lib")
int _tmain(int argc, _TCHAR* argv[])
{
::CoInitialize(NULL);
HRESULT hr = S_OK;
UINT nMsg = ::RegisterWindowMessage(_T("WM_HTML_GETOBJECT"));
LRESULT lRes = 0;
::SendMessageTimeout((HWND)0x000711FA, nMsg, 0L, 0L, SMTO_ABORTIFHUNG, 1000, (PDWORD)&lRes);
CComPtr<IHTMLDocument2> spDoc;
hr = ObjectFromLresult(lRes, IID_IHTMLDocument2, 0, (void**)&spDoc);
if (FAILED(hr))
return -1;
CComPtr<IHTMLElementCollection> spElementCollection;
hr = spDoc->get_all(&spElementCollection);
if (FAILED(hr))
return -2;
long lElementCount;
hr = spElementCollection->get_length(&lElementCount);
if (FAILED(hr))
return -3;
VARIANT vIndex; vIndex.vt = VT_I4;
VARIANT vSubIndex; vSubIndex.vt = VT_I4; vSubIndex.lVal = 0;
for (vIndex.lVal = 0; vIndex.lVal < lElementCount; vIndex.lVal++)
{
CComPtr<IDispatch> spDispatchElement;
if (FAILED(spElementCollection->item(vIndex, vSubIndex, &spDispatchElement)))
continue;
CComPtr<IHTMLElement> spElement;
if (FAILED(spDispatchElement->QueryInterface(IID_IHTMLElement, (void**)&spElement)))
continue;
CComBSTR outerHTML;
spElement->get_outerHTML(&outerHTML);
OutputDebugStringW(outerHTML);
}
::CoUninitialize();
return 0;
}
取得窗口的DOM如下：
將其輸出到文件，自行添上</BODY></HTML>即為完整的內容。不過需要記得的是Layout等元素只在打印預覽中有效，所以單獨提取出來崩潰不了也不要太疑惑，這里只是為了方便了解預覽中最終的DOM分布情況而已。
接下來，讓我們復現崩潰吧。打開map.yahoo.co.jp，訪問出現崩潰的代碼，右鍵預覽。只不過這次我們使用緩存文件的方式來精簡代碼。預覽后，從%TEMP%下復制走所有新生成的HTM文件，然后調節打印預覽的比例為666%。在確定仍然可以崩潰之后，讓我們開始刪除無用數據，記下異常偏移e9b102（在我的機器上是這個數字，因為有些崩潰在精簡代碼時可能變成其他的崩潰，所以最好記下偏移地址，以免中途不知道從什么位置產生了新問題）。多次精簡之后，我們留下了下列代碼：
#!html
<!DOCTYPE HTML>
<HTML><HEAD>
</HEAD>
<BODY>
<DIV style="left: -5000px; top: -5000px; width: 10000px; height: 10000px; text-align: justify; position: absolute; z-index: 0;"><svg
xmlns="http://www.w3.org/2000/svg" style="position: relative;" viewBox="0 0 10000 10000"
width="10000" height="10000" />
</DIV>
</BODY></HTML>
而且精簡到這一步就可以發現，只要發起打印預覽，IE就會直接崩潰。所以，為了讓IE自動觸發崩潰，我們手寫一下調用print();即可。
#!html
<!DOCTYPE HTML>
<HTML><HEAD>
</HEAD>
<BODY>
<DIV style="left: -5000px; top: -5000px; width: 10000px; height: 10000px; text-align: justify; position: absolute; z-index: 0;"><svg
xmlns="http://www.w3.org/2000/svg" style="position: relative;" viewBox="0 0 10000 10000"
width="10000" height="10000" />
</DIV>
<script>print();</script>
</BODY></HTML>
跟隨調試可以發現，崩潰位置維持不變：
#!bash
0:040> g
(24c8.2960): Access violation - code c0000005 (!!! second chance !!!)
eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=045c9220 edi=0a68eeac
eip=6537b102 esp=0a68eea4 ebp=0a68eeb8 iopl=0 nv up ei pl zr na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246
MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree+0x16:
6537b102 8b33 mov esi,dword ptr [ebx] ds:002b:00000000=????????
接下來讓我們看看打印預覽窗口的DOM結構。因為DIV的STYLE屬性是觸發崩潰的關鍵條件之一，但是我們又想拿到預覽窗口的DOM，所以我們得做一些改動，先手動刪除部分STYLE，然后預覽，這時，便可使用我們之前的程序抓出DOM。
篇幅考慮我就不扯淡再去看這個DOM了，直接以上述精簡后的代碼開始分析工作。
在崩潰后查看崩潰棧如下：
#!bash
0:033> kvn
# ChildEBP RetAddr Args to Child
00 0b2df530 64c7b6b7 0b2df75c 0b2df75c 64c7b63a MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree+0x16 (FPO: [Non-Fpo])
01 0b2df774 645de05b 0b2df7bc 0b2df79a 0b2dfb3c MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0x2b2eb
02 0b2df860 64b4110c 0b2dfb3c 0b2dfb3c 0b2dfb3c MSHTML!Layout::FlowBoxBuilder::BuildBoxItem+0x89 (FPO: [1,51,4])
03 0b2df87c 64b410d7 0b2dfb3c 0d82d0e0 0b2df8e4 MSHTML!Layout::LayoutBuilder::BuildBoxItem+0x2e (FPO: [Non-Fpo])
04 0b2df88c 64b40193 0b2dfb3c 0b2df908 64e657d0 MSHTML!Layout::LayoutBuilder::Move+0x57 (FPO: [Non-Fpo])
05 0b2df8e4 65358d8d 0d83264c 00000000 0d83264c MSHTML!Layout::LayoutBuilderDriver::BuildElementLayout+0xce (FPO: [Non-Fpo])
06 0b2df974 65359137 ffffffff 00000001 04c29ab4 MSHTML!Layout::MultiFragmentBoxBuilder::BuildCrossFragmentPositionedElement+0x1c3 (FPO: [Non-Fpo])
07 0b2df9d4 64ec4753 0b2dfa24 0d82d020 0d82cff0 MSHTML!Layout::MultiFragmentBoxBuilder::PositionAndArrangeCrossFragmentAbsolutePositionedElement+0x17e (FPO: [Non-Fpo])
08 0b2dfa2c 645d06b0 0d7e8ba0 04c29ab4 0b2dfb3c MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0xce2e3
09 0b2dfb14 645d72b9 0b2dfb3c 0b2dfb48 645d6ae0 MSHTML!Layout::PageCollection::LayoutPagesCore+0x37e (FPO: [Non-Fpo])
0a 0b2dfb40 65340900 65340760 0b2dfb88 0d832648 MSHTML!Layout::PageCollection::LayoutPages+0xca (FPO: [Non-Fpo])
0b 0b2dfb7c 64a9ec7e 00100000 04c29500 00000000 MSHTML!Layout::PageCollection::DoLayout+0x1a0 (FPO: [1,9,4])
0c 0b2dfbcc 64592161 00100000 64a7d7f0 00000000 MSHTML!CView::ExecuteLayoutTasks+0x159 (FPO: [Non-Fpo])
0d 0b2dfc24 64a7d840 00000000 64a7d7f0 0b2dfc54 MSHTML!CView::EnsureView+0x3bb (FPO: [1,15,4])
0e 0b2dfc44 64585813 04c29b38 00000000 00000001 MSHTML!CView::EnsureViewCallback+0x50 (FPO: [Non-Fpo])
0f 0b2dfc8c 6456d52c 3f72ceb5 00000000 6456cc90 MSHTML!GlobalWndOnMethodCall+0x17b (FPO: [Non-Fpo])
10 0b2dfce0 769f62fa 000825e0 00008002 00000000 MSHTML!GlobalWndProc+0x103 (FPO: [Non-Fpo])
11 0b2dfd0c 769f6d3a 6456cc90 000825e0 00008002 USER32!InternalCallWinProc+0x23
12 0b2dfd84 769f77c4 0539315c 6456cc90 000825e0 USER32!UserCallWinProcCheckWow+0x109 (FPO: [Non-Fpo])
13 0b2dfde4 769f788a 6456cc90 00000000 0b2dfe40 USER32!DispatchMessageWorker+0x3bc (FPO: [Non-Fpo])
14 0b2dfdf4 6507e640 0b2dfe24 0b2dfe4c 6629d470 USER32!DispatchMessageW+0xf (FPO: [Non-Fpo])
15 0b2dfe40 6ed93a31 05c7ab90 00000000 00000000 MSHTML!ModelessThreadProc+0x1a0 (FPO: [1,13,4])
MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree是一個Thiscall，代碼十分簡單，就是調用自己一個成員函數：
#!cpp
int __thiscall CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree(void *this, int a2, int a3, int a4, float a5)
{
return (*(int (__stdcall **)(_DWORD, int, _DWORD, _DWORD, _DWORD, _DWORD))(*(_DWORD *)this + 216))(
0,
a3,
0,
0,
LODWORD(a5),
0);
}
查看函數代碼，很明顯，this指針為null。
#!bash
0:033> uf .
MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree:
6537b0ec 8bff mov edi,edi
6537b0ee 55 push ebp
6537b0ef 8bec mov ebp,esp
6537b0f1 d94514 fld dword ptr [ebp+14h]
6537b0f4 33c0 xor eax,eax
6537b0f6 53 push ebx
6537b0f7 56 push esi
6537b0f8 57 push edi
6537b0f9 8bfc mov edi,esp
6537b0fb 8bd9 mov ebx,ecx ; ebx = ecx = this
6537b0fd 50 push eax
6537b0fe 51 push ecx
6537b0ff d91c24 fstp dword ptr [esp]
6537b102 8b33 mov esi,dword ptr [ebx] ; esi = *ebx
查看上一層
#!bash
0:033> ub .
MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0x2b2d4:
64c7b6a0 83ec08 sub esp,8
64c7b6a3 d95c2404 fstp dword ptr [esp+4]
64c7b6a7 51 push ecx
64c7b6a8 51 push ecx
64c7b6a9 8b08 mov ecx,dword ptr [eax]
64c7b6ab e8307699ff call MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent (64612ce0)
64c7b6b0 8bc8 mov ecx,eax
64c7b6b2 e835fa6f00 call MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree (6537b0ec)
很明顯MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent返回了NULL。
#!cpp
int __thiscall Layout::LayoutBox::GetDisplayNodeAsParent(void *this)
{
int pThisVar; // [email protected]
int nResult; // [email protected]
int v3; // [email protected]
int v4; // [email protected]
int v5; // [email protected]
pThisVar = (*(int (**)(void))(*(_DWORD *)this + 788))();
nResult = pThisVar;
if ( !pThisVar )
goto Cleanup;
v3 = *(_DWORD *)(pThisVar + 28);
v4 = pThisVar;
if ( *(_BYTE *)(v3 + 56) & 1
&& !*(_BYTE *)(*(_DWORD *)(__readfsdword(44) + 4 * LODWORD(_tls_index)) + 36)
&& *(_DWORD *)(v3 + 4) != *(_DWORD *)(pThisVar + 8) )
{
v5 = *(_DWORD *)(pThisVar + 4);
if ( !v5 )
v5 = nResult;
if ( v5 != nResult )
v4 = v5;
}
if ( !(*(_BYTE *)(v4 + 21) & 0x20) )
{
Cleanup:
nResult = NULL;
}
return nResult;
}
可以簡單跟蹤一下代碼看看到底是哪兒出現了問題。為了避免重復斷到斷點上（Layout的調用是十分頻繁的），可以
bp MSHTML!ModelessThreadProc
觸發后
bc 0
bp MSHTML!Layout::FlowBoxBuilder::BuildBoxItem
觸發后
bc 0
bp MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent
這樣就沒問題了
#!bash
0:031> g
Breakpoint 1 hit
eax=05618f80 ebx=0c07f060 ecx=0eebc4e0 edx=00000002 esi=0ee946e0 edi=0ee5ecb0
eip=64612ce0 esp=0c07f04c ebp=0c07f28c iopl=0 nv up ei pl nz ac po nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000212
MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent:
64612ce0 8bff mov edi,edi
0:031> k
ChildEBP RetAddr
0c07f048 64c7b6b0 MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent
0c07f28c 645de05b MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0x2b2e4
0c07f378 64b4110c MSHTML!Layout::FlowBoxBuilder::BuildBoxItem+0x89
0c07f394 64b410d7 MSHTML!Layout::LayoutBuilder::BuildBoxItem+0x2e
0c07f3a4 64b40193 MSHTML!Layout::LayoutBuilder::Move+0x57
0c07f3fc 65358d8d MSHTML!Layout::LayoutBuilderDriver::BuildElementLayout+0xce
再度跟蹤可以發現是
#!cpp
pThisVar = (*(int (**)(void))(*(_DWORD *)this + 788))();// MSHTML!Layout::SvgBox::GetDisplayNode //returns null
nResult = pThisVar;
if ( !pThisVar )
goto Cleanup; //return NULL(0);
查看GetDisplayNode，很明顯，校驗失敗，返回了0.
#!cpp
int __thiscall Layout::SvgBox::GetDisplayNode(int this)
{
int result; // [email protected]
if ( !(*(_BYTE *)(this + 56) & 4) || *(_BYTE *)(*(_DWORD *)(__readfsdword(44) + 4 * LODWORD(_tls_index)) + 36) )
result = *(_DWORD *)(this + 16);
else
result = 0;
return result;
}
加上對內存的跟蹤，我們可以斷定這是一個空指針問題。不過這倒也給了一個提醒——是否一些在網頁內不能觸發的問題，通過打印預覽就又可以做了呢？Fuzzer看來也可以加上這個策略，試一試打印預覽是否健壯。